It is often necessary or desirable for a person to exercise a particular muscle or group of muscles. For example, when a muscle is damaged, such as through injury or surgery, it is important to exercise the muscle to prevent atrophy and to strengthen the muscle for normal use. Further, people exercise healthy muscles to increase strength and to maintain an active and healthy lifestyle, as well as to improve their appearance. Various routines have been developed to exercise different muscle groups by forcing the muscles to contract and extend under a load, such as by moving a free weight against the force of gravity or by moving a pad or a sled whose movement is resisted by an exercise machine.
One exercise that has been developed to exercise the leg muscles is known as the leg press. A typical leg press exercise machine includes a footplate that moves relative to a seat. The user sits in the seat and places her feet on the footplate such that her legs are initially in a contracted or bent position. As the user extends her legs from the contracted position, the footplate is pushed away from the seat. The footplate typically is coupled to a resistance means that provides a reactive force against the force applied by the user.
Currently, leg press exercise machines having features similar to those disclosed in Jones, U.S. Pat. No. 5,106,080, and Simonson et al., U.S. Pat. No. 5,263,914, include an adjustable seat for accommodating users having different body sizes and leg lengths. The position of the seat relative to the footplate is adjusted prior to the commencement of exercise such that the user can exercise over a full range of motion. Alternatively, the footplate may be disposed at various initial positions with respect to a fixed seat.
Counterbalancing mechanisms, such as that disclosed in U.S. Pat. No. 3,858,873, are included in exercise machines in an attempt to overcome the inherent friction, gravity or weight resistance in operating the machine. Such a counterbalance, if implemented properly, would enable a user to exercise or train using zero or very small resistance loads. Further, the weight indicated on the resistance mechanism, such as a weight stack, would reflect accurately the weight resistance overcome by the user.
Leg press machines, however, do not provide an effective counterbalance over the full range of motion, particularly in view of the different initial positions for exercisers of varying stature. As the footplate is moved through the full range of motion, the position of the counterbalance mechanism and its counterbalance effect may change. This may require that the user exert more or less force than indicated on the resistance means. Further, traditional leg press machines allow adjustment for users of varying stature by sliding the seat toward the footplate. This may cause the orientation of the footplate with respect to the seat to change such that the user's foot is disposed in an awkward position during exercise. In particular, the footplate may be too high above the seat for short limbed users and too low for long limbed users. Further, the footplate may be tilted upward or downward too far such that a user will need to tilt her foot with respect to her foreleg to permit the foot to lie flat on the footplate. Consequently, the extension force will operate through the foot at an angle, rather than orthogonal to the bottom of the foot.